Ablation of the interior lining of a body organ is a procedure which involves heating the organ lining to temperatures which destroy the cells of the lining or coagulate tissue proteins for hemostasis. Such a procedure may be performed as a treatment to one of many conditions, such as chronic bleeding of the endometrial layer of the uterus or abnormalities of the mucosal layer of the gallbladder. Existing methods for effecting ablation include circulation of heated fluid inside the organ (either directly or inside a balloon), laser treatment of the organ lining, and resistive heating using application of RF energy to the tissue to be ablated.
U.S. Pat. No. 5,084,044 describes an apparatus for endometrial ablation in which a bladder is inserted into the uterus. Heated fluid is then circulated through the balloon to expand the balloon into contact with the endometrium and to ablate the endometrium thermally. U.S. Pat. No. 5,443,470 describes an apparatus for endometrial ablation in which an expandable bladder is provided with electrodes on its outer surface. After the apparatus is positioned inside the uterus, a non-conductive gas or liquid is used to fill the balloon, causing the balloon to push the electrodes into contact with the endometrial surface. RF energy is supplied to the electrodes to ablate the endometrial tissue using resistive heating.
These ablation devices are satisfactory for carrying out ablation procedures. However, because no data or feedback is available to guide the physician as to how deep the tissue ablation has progressed, controlling the ablation depth and ablation profile with such devices can only be done by assumption.
For example, the heated fluid method is a very passive and ineffective heating process which relies on the heat conductivity of the tissue. This process does not account for variations in factors such as the amount of contact between the balloon and the underlying tissue, or cooling effects such as those of blood circulating through the organ. RF ablation techniques can achieve more effective ablation since it relies on active heating of the tissue using RF energy, but presently the depth of ablation using RF techniques can only be estimated by the physician since no feedback can be provided as to actual ablation depth.
Both the heated fluid techniques and the latest RF techniques must be performed using great care to prevent over ablation. Monitoring of tissue surface temperature is normally carried out during these ablation procedures to ensure the temperature does not exceed 100° C. If the temperature exceeds 100° C., the fluid within the tissue begins to boil and to thereby produce steam. Because ablation is carried out within a closed cavity within the body, the steam cannot escape and may instead force itself deeply into the tissue, or it may pass into areas adjacent to the area intended to be ablated, causing embolism or unintended burning.
Moreover, in prior art RF devices the water drawn from the tissue creates a path of conductivity through which current traveling through the electrodes will flow. This can prevent the current from traveling into the tissue to be ablated. Moreover, the presence of this current path around the electrodes causes current to be continuously drawn from the electrodes. The current heats the liquid drawn from the tissue and thus turns the ablation process into a passive heating method in which the heated liquid around the electrodes causes thermal ablation to continue well beyond the desired ablation depths.
Another problem with prior art ablation devices is that it is difficult for a physician to find out when ablation has been carried out to a desired depth within the tissue. Thus, it is often the case that too much or too little tissue may be ablated during an ablation procedure.
It is therefore desirable to provide an ablation device which eliminates the above-described problem of steam and liquid buildup at the ablation site. It is further desirable to provide an ablation method and device which allows the depth of ablation to be controlled and which automatically discontinues ablation once the desired ablation depth has been reached.